network engineering, system administration, security tools

Many times we (network engineers) hear the complaint “the network is working, but it is terribly slow”. This is often one user’s perception of a perfectly working network however, other times there is something to the complaint. One thing to check is if that particular user’s switchport is reporting any errors. Let’s take a look at the error counters on a typical switchport.

When I was a younger engineer I used to look at output like this and have literally no idea what any of it meant. I just wanted to make sure that there weren’t tons of numbers in the output. After working in the field for awhile I look at this output differently. Each type can point you in the direction of what’s causing the error. Below I’ll list some common causes for each of these error types. Admittedly I don’t have all of these memorized, but as with all things if you don’t have it memorized, you just have to know where to find it.

Note: These errors can be caused by a variety of things. I’m only listing the most common issues and solutions I have seen.

Carri-SenCause: This error counter is incremented each time the switch tries to send data on a half duple link. With half duplex the port has to check the wire to ensure its open prior to sending the frame.Check: Duplex settings

GiantsCause: Frame exceeds size of 1518 bytes and has a bad FCSCheck: Device sourcing the frames

This post obviously wasn’t meant to tell you absolutely everything about frame and switchport errors. However, hopefully it has put you on the right track as far as troubleshooting port errors is concerned!